In order to better control the potential genotoxic impurities in labetalol hydrochloride and ensure the safety of medication, a high-performance liquid chromatography-mass spectrometry(HPLC-MS/MS) method was established to detect potential genotoxic impurities N-nitroso-labetalol in labetalol hydrochloride. The liquid chromatographic conditions were as following: the chromatographic column was Waters ACQUITY UPLC CSH C18(150 mm × 3.0 mm, 1.7 μm), mobile phase A was 0.01 mol/L ammonium formate -0.1% formic acid aqueous solution, mobile phase B was acetonitrile solution, the gradient elute was adopted, flow rate was 0.5 mL/min, the column temperature was 50 ℃, and the injection volume was 10 μL. Mass spectrometry conditions were established by using the electrospray ionization source as the ion source, negative ion mode and the multiple reaction monitoring mode, so that N-nitroso-labetalol in labetalol hydrochloride was quantified. The results indicate that the calibration curves is in good linearity in the range of 1.01~100.60 ng/mL; The recoveries (n=3) at low, middle and high spiked concentrations are within 96.84%~99.53%; The limit of detection is 0.01 ng/mL, and the limit of quantification is 0.03 ng/mL; The amount of N-nitroso-laelalol in six batches of the hydrochloride samples is 0.37~0.79 ng/mL. The proposed method is sensitive and accurate, and can be used for the quantification of N-nitroso-labetalol in labetalol Hydrochloride, providing some reference for the quality control of labetalol hydrochloride.